I just installed these in my 2002 Maxima, and they are amazing! A few things to keep note of, however:
These tweeters are highly directional. This is actually a really good thing in a car, since it reduces reflections that can reduce the clarity of the sound. I've also noticed excellent stereo separation. However, to get these benefits, the tweeters do need to be pointed at your ears vertically. (If you look at the tweeter's orientation in the product photo, it disperses widely in the horizontal dimension, but narrowly in the vertical.) This is tricky in a car, due to the size and shape of the tweeter. Most people install them into the kick panel. I drive a stick, so I need the kick panel for my foot, so I fashioned mounts out of 1/2" MDF covered with speaker carpeting in the same basic location pointing 45 degrees upward. It can be done, but where and how depends on the car. In the rear, I have them on the rear deck pointing up at the rear glass which reflects the sound forward at ear level. After experimenting with positioning, I found the best results with the tweeters oriented sideways, so that the dimension of wide dispersion would throw the sound forward and maintain the stereo separation.
Another thing to consider is that these are 8-ohm speakers, so they will draw about half the power than a 4-ohm speaker would. You'll want to either pair them with an 8-ohm woofer with the same sensitivity (94 dB) or a 4-ohm woofer with 3 dB lower sensitivity (91 dB). Keep the impedance in mind when designing the crossover.
Finally, a car can be a harsh environment for a speaker, especially if they are mounted near the floor. I covered mine with speaker grille cloth to protect it from flying debris particles with good results.